Cyclonic surface cleaning apparatus with sequential filtration members

ABSTRACT

A cyclonic surface cleaning apparatus incorporates a series of sequential physical filtration members to progressively remove smaller particulate matter whereby the physical filtration members collectively have a longer in use time prior to being clogged, thereby permitting a longer operating time prior to the cleaning or replacement of the physical filtration members.

FIELD

This application relates to surface cleaning apparatus, such as vacuum cleaners.

BACKGROUND

Various types of vacuum cleaners are known in the art. Currently, many of the vacuum cleaners, which are sold for residential applications, utilize at least one cyclone as part of the air filtration mechanism. More recently, to obtain higher levels of filtration, cyclonic vacuum cleaners have been designed which utilize two cyclonic stages. An example is shown in Conrad (U.S. Pat. No. 6,782,585). As shown therein, a vacuum cleaner has a first cyclonic cleaning stage comprising a single first stage cyclone and a second cyclonic cleaning stage that is downstream from the first cyclonic cleaning stage and comprises a plurality of cyclones in parallel.

The plurality of second stage cyclones typically remove particulate matter finer than the particulate matter that is removed in the first cyclonic cleaning stage. Accordingly, the coarsest particulate matter that is entrained in an air stream is removed in the first cyclonic cleaning stage and finer particulate matter is removed in the downstream cyclonic cleaning stage. However, the air exiting the second cyclonic cleaning stage may still contain sufficient particulate matter to damage a suction motor positioned downstream from the second cyclonic cleaning stage. Accordingly, as disclosed in Conrad, a screen or filter may be positioned downstream from the second cyclonic cleaning stage and upstream from the suction motor. Further, a HEPA filter may be positioned downstream from the suction motor.

SUMMARY

In accordance with this invention, a surface cleaning apparatus uses a plurality of filtration members having varying filtration ability. In accordance with this embodiment, a surface cleaning apparatus utilizes a foam filter positioned downstream from a cyclone, a felt filter positioned downstream from the foam filter and a HEPA filter positioned downstream from the felt filter. Preferably, a screen is provided for the air outlet of a cyclone chamber. The suction motor of the surface cleaning apparatus is preferably provided downstream from the HEPA filter, but may be upstream of the HEPA filter.

An advantage of this design is that filtration materials having finer pore sizes are positioned downstream from a series of coarse filtration elements thereby extending the lifetime of the finer filter elements.

In accordance with this invention, there is provided a surface cleaning apparatus comprising:

-   -   (a) a dirty air inlet, a clean air outlet downstream, a fluid         flow passage extending from the dirty air inlet to the clean air         outlet;     -   (b) a suction motor provided in the fluid flow passage;     -   (c) a filtration apparatus downstream from the dirty air inlet         and comprising a cyclone having a cyclone outlet;     -   (d) a foam filter downstream from the cyclone outlet;     -   (e) a felt filter downstream from the foam filter; and,     -   (f) a HEPA filter downstream from the felt filter.

In one embodiment, the surface cleaning apparatus further comprises a screen downstream from the cyclone outlet and upstream from the foam filter. Preferably, the screen comprises an open wire mesh.

The screen may have a surface area that is 2 times, preferably at least about 5 times, more preferably at least about 10 times and, most preferably at least about 20 times, e.g. 20-50 times, the cross sectional area of the cyclone air outlet. It will be appreciated that the screen may be flat or may be curved, e.g., bowl shaped. The use of such a large screen enhances the time during which the vacuum surface cleaning apparatus may be used without having to clean or replace the screen. Further, by positioning the screen exterior to the cyclone chamber, a large screen may be provided without reducing the size of the cyclone chamber

In any embodiment, the cyclone outlet may comprise a vortex finder, the vortex finder may have an upstream end in the cyclone and the upstream end may be unobstructed.

In any embodiment, the cyclone outlet may have a shroud. Preferably, the shroud comprises an apertured end of the cyclone outlet.

In any embodiment, the suction motor may be positioned downstream from the HEPA filter. Alternately, the suction motor may be positioned upstream from the HEPA filter.

In any embodiment, the screen may be mounted in a housing having an outer wall that is transparent. Preferably, the outer wall is openable, e.g. a pivotally mounted door. Alternately, it may be removably mounted, such as by a screw thread or a bayonet mount, a snap fit or the like. Alternately, it may be slidably mounted or rotationally mounted.

In any embodiment, the foam filter, the felt filter and the HEPA filter may be individually or selectively removably mounted in the surface cleaning apparatus and, preferably removable as a unit.

In any embodiment, each layer of physical filtration media may be selected to remove a particular size range of particles that is larger than that of the next downstream, layer of filtration material.

In any embodiment, the cyclone may have a separation efficiency for IEC dirt of 98% of particles that are from 3 to 5 microns and at least 96.5% of particles that are from 1-2 microns.

In any embodiment, the foam may have a separation efficiency of 70-85% of particles that are 1-2 microns and 30-50% of particles that are 0.3-0.9 microns.

In any embodiment, the felt may have a separation efficiency of 70-85% of particles that are 0.5-0.9 microns and 30-50% of particles that are 0.3 microns.

It will be appreciated by those skilled in the art that any of the embodiments may be used individually or in a single surface cleaning apparatus, as exemplified in a preferred embodiment described herein, or in any particular sub-combination. Accordingly, any two or more embodiments may be used in a single surface cleaning apparatus. In addition, any of the optional features described herein may be used in combination with any alternate embodiment or sub-combination or combination of alternate embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the instant invention will be more fully and completely understood in conjunction with the following description of the preferred embodiments of the invention in which:

FIG. 1 is a side elevational view of a preferred embodiment of a vacuum cleaner in accordance with this design wherein the outer casing surrounding the cyclone and forming an outer wall of a dirt collection chamber is optionally transparent;

FIG. 2 is a perspective view from the front and the right side of the vacuum cleaner of FIG. 1;

FIG. 3 is a cross-section along the line 3-3 in FIG. 2;

FIG. 4 is a schematic drawing of the vacuum cleaner of FIG. 1 showing the airflow passage therethrough;

FIG. 5 is a perspective view from the bottom of the vacuum cleaner of FIG. 1 wherein the bottom of the first and second housings is open;

FIG. 6 is a perspective view of the bottom of the vacuum cleaner of FIG. 1 wherein the first and second housings are closed but an access door is open; and,

FIG. 7 is a longitudinal section through an alternate embodiment of a vacuum cleaner in accordance with this invention.

DETAILED DESCRIPTION

As shown in FIGS. 1-6, a surface cleaning apparatus comprises a vacuum cleaner 10 having a filtration apparatus having at least one cyclone. The filtration apparatus may be of any design or configuration. As exemplified, surface cleaning apparatus 10 has a first housing 12 and a second housing 14. First housing 12 comprises at least one cyclone 16 and a dirt collection chamber 18 and second housing 14 houses the filtration members and the suction motor. Dirty air entrained in dirty air inlet 38 travels through the filtration apparatus, through suction motor 26 and exits the surface cleaning apparatus via clean air outlet 60. As shown in FIG. 7, a surface cleaning apparatus 10 has a first cyclonic cleaning stage comprising a single cyclone 150 having a dirt collection chamber 152 and a second cyclonic cleaning stage comprising a plurality of second stage cyclones 154 in parallel.

It will be appreciated that, surface cleaning apparatus may be a vacuum cleaner, a carpet extractor, a bare floor cleaner or the like. As exemplified, the surface cleaning apparatus is hand held. However the surface cleaning apparatus may be configured as an upright vacuum cleaner, a stick vacuum cleaner, a canister vacuum cleaner, a back pack or shoulder strap vacuum cleaner or other configuration known in the art. The surface cleaning apparatus may have a single cyclonic cleaning stage, which may be of any construction known in the art, or a plurality of cyclonic cleaning stages, each of which may be of any construction known in the art, e.g. they may comprise a single cyclone or a plurality of cyclones in parallel.

In accordance with this invention, a series of filtration members are positioned in series downstream from the cyclone chamber of cyclone 16, or alternately downstream from the outlet of the last cyclonic cleaning stage. The filtration members comprise a foam filter 20, a felt filter 22 downstream from foam filter 20 and a HEPA filter 24 downstream from felt filter 22. Preferably, all of these filters are positioned upstream from suction motor 26. Alternately, one or more of these filters may be positioned downstream from suction motor 26. In particular HEPA filter 24 may be downstream from suction motor 26 (see for example FIG. 7). Accordingly, a plurality of filtration members, each of which have a finer filtration capacity (e.g. smaller pores) than the previous filter, are provided in series in the downstream direction.

For example, the foam filter may be an open cell foam made from materials currently used to manufacture foam filters for vacuum cleaners and may be selected to have pore sizes from 0.25-5 microns and may have a mean pore size of 2 microns. Accordingly, the foam will filter particles larger than 5 microns and some of the particles that are between 0.25-5 microns. The felt filter may be woven or non-woven and may be made from plastic, preferably rayon, nylon, polypropylene or a combination thereof. The felt may be selected to have pore sizes from 0.1-2.5 microns and may have a mean pore size of 1 micron. Accordingly, the felt will filter particles larger than 2.5 microns and some of the particles that are between 0.1-2.5 microns. HEPA filtration is typically defined as removal of 99.97% of particles larger than 0.3 microns.

In a preferred embodiment, cyclone 16, or the cyclonic cleaning stages combined (e.g. cyclone 16 in FIG. 1 or cyclones 150 and 152 in FIG. 7), may achieve a separation efficiency for IEC dirt as specified as IEC 60312, which is representative of household dirt, of 98% of particles that are from 3 to 5 microns and at least 96.5% of particles that are from 1-2 microns. By removing a high percentage of particles in this size range, the foam will not prematurely clog. Similarly, the foam preferably has a separation efficiency of 70-85% of particles that are 1-2 microns and 30-50% of particles that are 0.3-0.9 microns. By removing a high percentage of particles in this size range, the felt will not prematurely clog. Similarly, the felt preferably has separation efficiency of 70-85% of particles that are 0.5-0.9 microns and 30-50% of particles that are 0.3 microns. By removing a high percentage of particles in this size range, the HEPA will not prematurely clog.

It will be appreciated that each of the foam and the felt may have varying pore sizes as long as each filters a significant amount of particles that would prematurely clog the next sequential filter media. Accordingly, the filtration specification of each layer of filtration media is selected to be complimentary to the next sequential layer of filtration media and may essentially remove particles that are larger than those that are within the size range targeted for the next sequential filtration media. In other words, each layer of filtration material is selected to remove a particular size range of particles. Accordingly, each upstream layer is selected to remove a particular size range of particles that is larger then that of the next downstream layer of filtration material.

In a preferred embodiment, foam filter 20, felt filter 22 and HEPA filter 24 are removably mounted as a unit (e.g., they may be mounted in a filter housing or directly secured to each other). For example, when second housing 14 is opened, e.g., by opening bottom 66, foam filter 20, felt filter 22 and HEPA filter 24 may be removed together. Alternately, they may be separately removable. In either embodiment, it is preferred that they are separable when removed so that individual filters may be cleaned and/or replaced. Alternately, the foam filter 20, felt filter 22 and HEPA filter 24 may be an assembly that is replaceable as a unit, e.g., a new filter housing containing all three filters may be inserted.

It will be appreciated that each of the foam filter 20, felt filter 22 and HEPA filter 24 may comprise a single filter or a plurality of filters. For example, foam filter 20 may comprise a series of layers of foam.

Preferably, a screen 78 is provided upstream from foam filter 20 and preferably downstream from the cyclone chamber of cyclone 16, or alternately downstream from the outlet of the last cyclonic cleaning stage. For example, it may be adjacent outlet 52 of outlet or vortex finder 36, e.g., connected thereto, or positioned in the air flow path, e.g., filtration chamber 80, such that air flow is caused to pass therethrough. It will be appreciated that screen 78 may be provided immediately upstream of foam filter 20, e.g., it may be provided below foam filter 20 in second housing 14.

Optionally, a shroud (e.g. a perforated or apertured plastic cover) may be provided surrounding or overlying inlet 50 of outlet 36.

In the exemplified embodiment, cyclone 16 has a dirt outlet 28 and an optional impingement surface 30 spaced from dirt outlet 28 in dirt collection chamber 18. As shown in FIG. 3, impingement surface 30 is preferably spaced a distance D from outlet 28 wherein distance D is from 8 to 30 millimeters and, preferably from 12 to 25 millimeters. It will be appreciated that impingement member 30 may be mounted to lid 32 of dirt collection chamber 18. Alternately, impingement member 30 may be mounted to a sidewall of dirt collection chamber 18 and/or cyclone 16.

As exemplified in FIG. 3, cyclone 16 is an inverted cyclone. Accordingly, cyclone 16 has a lower air inlet 34 and a lower air outlet 36. Air inlet 34 is positioned downstream from dirty air inlet 38 of surface cleaning nozzle 40. Surface cleaning nozzle 40 may be any surface cleaning nozzle known in the art. Air inlet 34 of cyclone 16 may be in airflow communication with surface cleaning nozzle 40 in any manner known in the art. The exact structure of surface cleaning nozzle 40 and the communication passage between surface cleaning nozzle 40 and air inlet 34 will vary depending on if the surface cleaning apparatus is an upright vacuum cleaner, canister vacuum cleaner or, as exemplified, a portable hand held vacuum cleaner.

In operation, air will enter cyclone 16 through inlet 34 and travel upwardly, as exemplified in FIG. 4. The air will then travel downwardly to exit cyclone 16 via outlet 36. As shown in FIG. 4 by the hatched arrows, dirt will exit upwardly through outlet 28 and deposit on dirt collection chamber floor 42. In addition, some of the heavier particulate matter may not be entrained in the air stream and may be deposited on cyclone floor 44.

In an alternate embodiment, it will be appreciated that cyclone 16 need not be inverted. Cyclone 16 may be any cyclone with a dirt outlet provided wherein, preferably, impingement member or members are positioned spaced from the dirt outlet. The cyclone may accordingly be an upright cyclone or a cyclone having a single direction of travel of the air.

As exemplified, cyclone 16 is a frustoconical cyclone having cylindrical portion 46 and frustoconical portion 48. Alternately, or in addition to the orientation of cyclone 16, it will be appreciated that cyclone 16 may be cylindrical, entirely frustoconical or any other shape known in the art.

As exemplified in FIG. 3, cyclone outlet 36 of cyclone 16 comprises a vortex finder that extends inwardly into the cyclone chamber defined by cyclone 16. Outlet 36 preferably comprises a generally cylindrical passage, i.e. vortex finder, having an inlet 50 and an outlet 52. It will be appreciated that, in an alternate embodiment any outlet known in the art for cyclones may be utilized.

In some embodiments, inlet 50 may be covered by a screen, shroud or filter as in known in the art. However, it is preferred that vortex finder 36 is unobstructed, i.e., no screen, shroud or filter is provided on inlet 50. Accordingly, as exemplified in FIG. 3, vortex finder 36 is not surrounded by a screen, shroud or filter and no physical separation member is positioned in the cyclone chamber of cyclone 16. Accordingly, no filtration or screen member interior of cyclone 16 requires cleaning. Elongate material such as hair or fibre can become adhered to a shroud, requiring the shroud to be manually cleaned. If the shroud is inside the cyclone chamber, then the chamber should be openable sufficiently to permit a user to insert their hand to clean the shroud, or to remove the shroud for cleaning. Accordingly, it will be appreciated that bottom 44 need not be openable to permit a screen or a shroud or filter associated with inlet end 50 of outlet 36 to be cleaned. Preferably, a screen is positioned downstream from cyclone 16 and upstream from the pre-motor filters. For example, a screen 78 is preferably provided.

As exemplified in FIGS. 1-6, vacuum cleaner 10 comprises a hand held vacuum cleaner. Accordingly, vacuum cleaner 10 may be provided with handle 54, which is affixed to lid 32 and lid 58 of second housing 14. Handle 54 may alternately be affixed to any other portion or portions of vacuum cleaner 10 as is known in the art. Optionally, as exemplified, on/off switch 56 may be provided on handle 54. On/off switch 56 may alternately be provided on any other portion of vacuum cleaner 10.

As exemplified in FIG. 3, suction motor 26 is positioned in second housing 14, preferably with a suction fan provided below the electric motor. Clean air outlet 60 is provided downstream from suction motor 26. An optional post-motor filter may be provided downstream from suction motor 26, such as in post-motor filter housing 62, which may be accessible via post motor filter housing door 64, which could be pivotably mounted to second housing 14.

As exemplified, dirt collection chamber 18 surrounds cyclone 16. Accordingly, cyclone 16 may be positioned in dirt collection chamber 18 and, preferably, generally centrally therein. Accordingly, vacuum cleaner 10 is preferably configured such that the dirt collected on floor 44 of cyclone 16 is emptied at the same time as dirt collected on floor 42 of dirt collection chamber 18. Accordingly, floor 42 and floor 44 are both movable and connected to each other whereby both floor 42 and 44 are concurrently movable such that dirt collection chamber 18 and cyclone 16 are concurrently emptied.

As exemplified in FIG. 5, floors 42 and 44 may comprise a pivoting bottom 66 of first housing 12 and, alternately, of the filtration apparatus (e.g. housings 12 and 14 of this embodiment). Accordingly, as seen in FIG. 5, when floors 42 and 44 are opened, both cyclone 16 and dirt collection chamber 18 may be emptied by holding vacuum cleaner 10 in the upright position (as shown in FIG. 1). Accordingly, the dirt will fall out of collection chamber 16 and cyclone 16 and will fall downwardly off of floors 42 and 44.

As shown in FIG. 5, housings 12 and 14 have a pivoting bottom 66, which is secured to each of housings 12 and 14 by a pivot 68. In the closed position exemplified in FIGS. 1 and 4, pivoting bottom 66 is secured in position by latch 70. Latch 70 has a button 72 which, when pressed, causes arm 74 to move outwardly thereby disengaging a flange provided on the bottom end of arm 74 from flange 76 provided on pivoting bottom 66. A gasket or other sealing member may be provided at the interface of housings 12 and 14 and pivoting bottom 66 to provide an air tight or fluid tight seal. It will be appreciated that bottom 66 may be moveable in any other direction by any other means known in the art and may optionally be removable from housings 12, 14. Further, bottom 66 may be moveably secured in position by any other means known in the art and need not be connected to surface cleaning apparatus 10 for relative motion thereto.

As exemplified in FIG. 5, outlet 36 is provided as part of floor 42, and is preferably integrally molded therewith. In an alternate embodiment, it will be appreciated that outlet 36 need not be removable from cyclone 16 with floor 42.

In an alternate embodiment, it will be appreciated that only floors 42 and 44 may be pivotably mounted to housing 12. In such an embodiment, foam filter 20 may remain sealed when cyclone 16 and dirt collection chamber 18 are emptied. In such a case, the housing that contains foam filter 20 may be separately opened. In an alternate embodiment, a side-by-side design as exemplified in FIG. 1 need not be utilized. In such a case, floor 42 and floor 44 may comprise the entire floor of the filtration assembly.

If bottom 66 opens both housings 12 and 14, then it will be appreciated that dirt positioned on the upstream surface of filter 20 will be emptied when bottom 66 is opened.

Preferably a screen is provided adjacent outlet 36 and, preferably, in sealing engagement with outlet 52. Screen 78 may be mounted in a housing (filtration chamber 80), having an outer wall all or a portion of which is preferably transparent and positioned downstream from vortex finder 36. Referring to FIG. 3, screen 78 is positioned spaced from and in sealing engagement with rear surface 84 of floor 44 and overlies outlet 52. Accordingly, air that exits outlet 36 travels through screen 78. The air then travels through filtration chamber 80 and travels laterally to outlet 86, which is in air flow communication with headspace 88 below filter 20.

Preferably, screen 78 may be an open mesh screen, e.g., a wire mesh screen or, alternately, a plastic mesh screen.

An access door 82 may be provided to permit access to screen 78 such that screen 78 may be cleaned. Access door 82 may be any door that is movably mounted in overlying relationship to filtration chamber 80. As exemplified in FIG. 6, access door 82 comprises the lower half of filtration chamber 80 and is pivotally mounted by pivot 90 to pivoting bottom 66, and is secured in position by a latch 120. Latch 120, for example, may have a button 122 which, when pressed, causes arm 124 to move outwardly thereby disengaging a flange on the bottom end of arm 124 from flange 92 provided on the front end of access door 82. A sealing gasket or other sealing member known in the art may be utilized to provide an air tight or fluid tight seal for filtration chamber 80. Any other securing member known in the art may be used. Further door 82 may be removable and need not be connected to surface cleaning apparatus 10 for relative motion thereto.

Preferably, screen 78 is mounted and, more preferably, movably mounted and, most preferably, removably mounted to access door 82. As shown in FIG. 6, screen 78 is pivotally mounted to the inner surface of access door 82. Accordingly, when a user desires to clean screen 78, it may be pivoted in the direction shown by arrow A in FIG. 6 to an open or cleaning position. It will be noticed that access door 82 may be opened independently of pivoting bottom 66. In an alternate embodiment, it will be appreciated that a pivoting bottom 66 need not be provided.

Preferably, at least a portion of and, more preferably, all of access door 82, which as exemplified is the outer wall of filtration chamber 80, is transparent. Accordingly, a user may lift the vacuum cleaner, invert the vacuum cleaner or tilt the vacuum cleaner on its side to view screen 78 and determine whether screen 78 requires cleaning or, alternately, replacement.

The use in a vacuum cleaner of a foam filter, a felt filter and a HEPA filter in series, preferably with a screen upstream of the foam filter, may be used alone or in combination with one or more of the spacing of an impingement surface, an access door to permit cleaning or replacement of the screen, the screen being positioned downstream of a cyclone outlet and mounted in a housing which is transparent, a configuration to allow a cyclone chamber and a surrounding dirt collection chamber to be emptied concurrently, a bottom door that opens to expose the foam filter and permit the filters to be removed such that one or more of them may be cleaned or replaced, or any particular combination or sub-combination thereof.

It will also be appreciated that any of the aforementioned embodiments may be used singly or in any particular combination or sub-combination of the remaining features listed above.

Although the invention has been described in conjunction with specific embodiments thereof, if is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. 

1. A surface cleaning apparatus comprising: (a) a dirty air inlet, a clean air outlet downstream, a fluid flow passage extending from the dirty air inlet to the clean air outlet, (b) a suction motor provided in the fluid flow passage; (c) a filtration apparatus downstream from the dirty air inlet and comprising a cyclone having a cyclone outlet, (d) a foam filter downstream from the cyclone outlet; (e) a felt filter downstream from the foam filter; and, (f) a HEPA filter downstream from the felt filter.
 2. The surface cleaning apparatus of claim 1 further comprising a screen downstream from the cyclone outlet and upstream from the foam filter.
 3. The surface cleaning apparatus of claim 2 wherein the screen comprises an open wire mesh.
 4. The surface cleaning apparatus of claim 1 wherein the cyclone outlet comprises a vortex finder and the vortex finder has an upstream end in the cyclone and the upstream end is unobstructed.
 5. The surface cleaning apparatus of claim 1 wherein the cyclone outlet has a shroud.
 6. The surface cleaning apparatus of claim 5 wherein the shroud comprises an apertured end of the cyclone outlet.
 7. The surface cleaning apparatus of claim 1 wherein the suction motor is downstream from the HEPA filter.
 8. The surface cleaning apparatus of claim 1 wherein the suction motor is upstream from the HEPA filter.
 9. The surface cleaning apparatus of claim 2 wherein the screen is mounted in a housing having an outer wall that is transparent.
 10. The surface cleaning apparatus of claim 9 wherein the outer wall is openable.
 11. The surface cleaning apparatus of claim 1 wherein the foam filter, the felt filter and the HEPA filter are removably mounted in the surface cleaning apparatus.
 12. The surface cleaning apparatus of claim 11 wherein the foam filter, the felt filter and the HEPA filter are removable as a unit.
 13. The surface cleaning apparatus of claim 1 wherein each layer of physical filtration media is selected to remove a particular size range of particles that is larger then that of the next downstream layer of filtration material.
 14. The surface cleaning apparatus of claim 1 wherein the cyclone has a separation efficiency for IEC dirt of 98% of particles that are from 3 to 5 microns and at least 96.5% of particles that are from 1-2 microns.
 15. The surface cleaning apparatus of claim 14 wherein the foam has separation efficiency of 70-85% of particles that are 1-2 microns and 30-50% of particles that are 0.3-0.9 microns.
 16. The surface cleaning apparatus of claim 14 wherein the felt has a separation efficiency of 70-85% of particles that are 0.5-0.9 microns and 30-50% of particles that are 0.3 microns.
 17. The surface cleaning apparatus of claim 15 wherein the felt has a separation efficiency of 70-85% of particles that are 0.5-0.9 microns and 30-50% of particles that are 0.3 microns. 